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lambda

A utility for working with C-Libraries from C++

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Basic Examples

Using lambdas with capture as a function pointer

extern "C" void some_c_function(void (*callback)(int a))
{
    // ...
}

std::string some_string;

some_c_function(lambda::pointer_to([&](int)
{
    some_string = "Captured by reference!";
}));

A utility for passing void* user data

extern "C" void some_c_function(void (*callback)(int a, void* user_data), void* user_data)
{
    // ...
}

std::string some_string;
auto user_data = lambda::user_data(some_string);

some_c_function([](int a, void* data) {
    auto &[some_string] = decltype(user_data)::from(data).tuple();
    some_string = "Easy user-data!";
}, user_data);

For more examples, and some useful comments, you might want to take a look at the tests!

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Installation

Note
This library requires a C++20 capable compiler.

• FetchContent

  include(FetchContent)
  FetchContent_Declare(lambda GIT_REPOSITORY "https://github.com/Curve/lambda")
  
  FetchContent_MakeAvailable(lambda)
  target_link_libraries(<YourLibrary> lambda::ptr)

• Git Submodule

  git submodule add "https://github.com/Curve/lambda"

  # Somewhere in your CMakeLists.txt
  add_subdirectory("<path_to_lambda>")
  target_link_libraries(<YourLibrary> lambda::ptr)

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Windows

Q: Does this Library work on windows?
A: Yes

Q: Does this library work with MSVC?
A: Kind of, beware that lambda captures on MSVC are broken¹ and MSVC Versions below 19.36 are affected by a bug that causes compilation errors.

¹: This bug has already been reported and will hopefully be fixed with a new MSVC update.

❌ Broken	✅ Working
some_c_function(lambda::pointer_to([&]{/*...*/}));	auto fn_ptr = lambda::pointer_to([&]{/*...*/}); some_c_function(fn_ptr);

Q: Are there alternatives to MSVC?
A: Yes! I'd recommend to just use clang-cl